1. Field of the Invention
The present invention is in the field of sound synthesizers that produce sounds to simulate the sounds produced by an automobile or other motorized vehicle.
2. Description of the Related Art
Racing car games are available for use with televisions and computers. Driving simulators have become popular recently. For such games and simulators, synthesizers have been employed to produce engine sounds (e.g., engine firing sounds or driving sounds, including mechanical sounds and intake/exhaust sounds) to improve the impression that the “driver” is driving a real car. Conventionally, a so-called actual sound loop reproduction method has been commonly used for synthesizers. In such conventional synthesizers, several seconds of actual driving sounds (e.g., engine sounds) are recorded as a digital data during a normal operational state. Such drive sound data (i.e., engine sound data) is repetitively played by altering the pitch and sound volume depending on the operational state of the game or simulation.
In an exemplary system, the drive sound data in such an actual sound loop reproducing method is sampled at a sampling rate (i.e., a sampling frequency) of 44.1 kHz. Thus, a sound pressure value of the sampled sound is transmitted from an engine at a cycle (i.e., period) of about 2.268×10−5 second. The sequential group of sound pressure data sampled at this particular cycle is considered to be digital data for engine sound pressure waveforms (i.e., the sound data represented as the digital signal). A greater sampling rate can be used so that the reproduced sound pressure waveform is closer to the sound pressure waveform of the actual driving sound.
In reproducing such driving data as a driving sound corresponding to an operational state (i.e., an engine speed or an acceleration rate) of a vehicle, if a speed of the simulated drive unit at a particular operational state to be reproduced matches a speed of the actual drive unit at the normal operational state that is recorded as a digital signal, sound pressure waveforms that are the same as the driving sound at the normal operational state can be reproduced by reproducing the recorded sequential sound pressure data at the same reproduction rate as the sampling rate (namely, at the same reproduction cycle as the sampling cycle).
Conversely, for an operation to increase the revolution speed of the drive unit, the pitch of the reproduced sound is elevated to a higher pitch than the pitch of the actual driving sound that was recorded as a digital signal at the normal operational state. The increase in pitch is accomplished by elevating the sound reproduction rate (i.e., by shortening the reproduction cycle to elevate the reproduction frequency) and by increasing the frequency of the reproduction of the stored sequential sound pressure data by shortening the waveform in a time axis.
Further, for an operation to decrease the revolution speed of the drive unit, the sound is reproduced by modifying the pitch in proportion to the pitch of the decreasing speed of the drive unit by reducing the sound reproduction rate.
In this actual sound loop reproduction method, the sound can be reproduced as close to the actual sound as possible under the normal operation pattern which is proximate to the actually recorded speed of the drive unit. However, the sound reproduction is not so successful in a transitional period between two operational states and for other operational states beyond the particular operational state of the actually recorded sound. The reproduced sound turns out to be an unnatural sound even if the pitch and sound volume are modified.
A conventional solution for this problem is to record various types of actual driving sounds as drive sound data for a duration of several seconds. Particular drive sound data recorded at a particular operational state is selectively read out if it matches or if it is at least proximate to an operation corresponding to a certain driving operation. Then, this drive sound data for several seconds is repetitively reproduced by altering the pitch or volume. However, the storage of such various types of actual driving sounds leads to an increased capacity of the memory means. The expanded capacity of the memory means is an obstacle to providing inexpensive products.
In addition, such a conventional actual sound loop reproduction method requires the storage of different types of the engine sound depending on the number of cylinders and alignment of the cylinders. Such a requirement leads to an increase in the required memory capacity and to increased manufacturing costs.
There is another recent trend for the TV games and computer games. In such a recent trend, the game machines and personal computers are connected to a server through a communication line by which two operators can play against each other on line. For such online type games, pictures and sound data that require enormous memory capacity and thus tend to delay the progress of the game are previously stored in the game machines and personal computer.
For the online games in which two players play against each other through the communication lines, if the sound data capacity is increased, it takes more time to transfer the data. For example, for two seconds of data of 16-bit stereo data at a 44.1 kHz sampling frequency, the required memory capacity is approximately 353 kbytes. If such data is transferred at a rate of 64 kbps, it takes about three quarters of a minute to complete the transfer. In addition, plural segments of transferred sound data typically need to be transferred. As a result, it requires a long transfer time before the game actually begins. Thus, for the vehicle operating game, it is difficult to switch the type of synthesized sound when changing it to another game.
Conventionally, for the online games, the sound data is stored in advance in the game machines and personal computers from CD-ROMs and floppy disks. However, it may be sometimes overwhelming for a player to store each sound data because the player most likely plays a large number of different games. In addition, such sound data occupies major portions of the memory device of the game machines and personal computers.